46 FRANK R. LILLIE. 



blastic somites on this side, but not the ganglia and cord of these 

 somites (see Fig. i). The form of the embryo indicates that this 

 is true in part ; but there is a small myotome in the eighth post- 

 brachial somite of this side, and in the seventh the myotome is 

 quite as well developed as on the other side. It would appear 

 probable, then, that the most lateral portions of the seventh and 

 eighth postbrachial mesoblastic somites were destroyed, together 

 with the somatopleure lateral to this ; either the rudiments of the 

 hind limb were included in the destroyed parts, or their develop- 

 ment was prevented by the scar-tissue. It is impossible to say 

 whether or not the two somites concerned in the formation of the 

 left leg have formed more than the normal. 



The central nervous system terminates abruptly, except that 

 the ventral portion of the canal is continued back as a narrow 

 epithelial tube. The notochord extends some sections back of 

 the termination of the neural tube, showing that it has been added 

 to at its hind end since the operation. 



The Wolffian ducts are immensely enlarged (see figures). 

 There is no metanephric outgrowth. The allantois is entirely 

 absent. The alimentary canal is normal back to the defective 

 region and terminates in a band lying between the two Wolffian 

 ducts (Fig. 6). 



Experiment 18. 



The tail-bud of the embryo was just formed at the time of the 

 operation, and it was completely destroyed with a heated needle 

 (see operation diagram). The injury did not extend so far for- 

 ward as in the other cases mentioned and was asymmetrical 



(Fig. i). 



Fifty hours later the egg was reopened, and the embryo was 

 found living, the heart beating actively ; the vascular area covered 

 about one third of the yolk. 



Fig. 7 shows the embryo as it appeared from the under sur- 

 face of the blastoderm. It will be observed that the amnion 

 ceases with a free edge immediately in front of the hind-limbs ; 

 thus the tail-fold of the amnion destroyed by the operation has 

 not regenerated, nor is the allantois visible externally, as it always 

 is in normal embryos of this age. The hind-limbs appear normal ; 

 part of the tail at least is present. 



